The present invention relates to a liquid filled type vibration isolator which is aimed at isolating vibration in a specific frequency range, and in particular, to a liquid filled type vibration isolator incorporating a diaphragm and an orifice which are adapted to isolate vibration in two frequency ranges, that is, for example, an engine idling vibration range and an engine shake range, respectively, and which are incorporated in a partition member partitioning between a main chamber and an auxiliary chamber in the vibration isolator. Further, the present invention also relates to a liquid filled type vibration isolator which can prevent a dynamic spring constant from extremely increasing even though the engine idling vibration frequency varies caused by an increase in engine idling speed.
Among vibration isolators, engine mounts or the like for automobiles, have to cope with vibration over a wide frequency range since an engine as a power source is used under various conditions over a wide speed range from an idle speed to a maximum speed. Thus, there was proposed and have been well-known a switching and liquid filled type vibration isolator defining therein two liquid chambers which are communicated with each other through an orifice, and having a vibration isolating mechanism which is composed of a diaphragm configured to carry out free oscillation in response to variation in liquid pressure in the above-mentioned liquid chambers, a working chamber and the like, as disclosed in JP-A-4-77041.
By the way, in the above-mentioned prior art, the atmospheric pressure is led into the working chamber which is therefore set in a condition opened to the atmosphere, and a second diaphragm defining the working chamber is held in a free oscillation condition. With this arrangement, as to inputted engine idling vibration, variation in liquid pressure in the main chamber is absorbed through free oscillation of the second diaphragm in order to aim at absorbing and isolating the engine idling vibration. Meanwhile, as to the engine shake having a frequency range which is lower than that of the engine idling vibration, liquid is positively led from the main chamber through the orifice so as to effect a high damping characteristic. Thus, the above-mentioned prior art allows the orifice to serve as only a damping force exhibiting mechanism for damping the engine shake. Further, in addition to the first diaphragm partitioning between the auxiliary chamber and the air chamber, since the second diaphragm is provided, independent from the first diaphragm, and so forth, there has been raised such a problem that the overall manufacturing cost would inevitably increased, in view of assembling workability, parts control and the like.
The present invention is devised in order to solve the above-mentioned problems, and accordingly, an object of the present invention is to provide a liquid filled type vibration isolator which enables the above-mentioned orifice to damp the engine idling vibration and in which the first diaphragm is integrally incorporated with the second diaphragm in order to aim at reducing the overall manufacturing cost.
To the end, according to the present invention, there are provided the following arrangements. That is, according to a first aspect of the present invention, there is provided a liquid filled type vibration isolator comprising a first coupling member attached to an oscillating body, a second coupling member attached to a member on a vehicle body side, a rubber-like insulator provided between the first coupling member and the second coupling member, for absorbing vibration from the vibrating body, a main chamber having a chamber wall defined by a part of the insulator and filled therein with liquid, an auxiliary chamber communicated with the main chamber through the intermediary of a first orifice, and having a chamber wall apart of which is defined by the first diaphragm, a partition member partitioning between the main chamber and the auxiliary chamber, and a second diaphragm partitioning between a working chamber into which negative pressure or the atmospheric pressure is selectively introduced, wherein the second diaphragm defines the working chamber and has a rigidity for flexible stiffness which is higher than that of the first diaphragm defining the auxiliary chamber.
With this arrangement, according to the present invention, only one orifice is used for exhibiting a damping function against the engine shake, and as to the engine idling vibration, liquid within the orifice is subjected to resonance so as to aim at reducing the dynamic spring constant in this frequency range. As a result, with the use of only one orifice, it is possible to damp two kinds of vibration such as engine shake and engine idling vibration.
Next, according to a second a second aspect of the present invention, which is basically similar to the first aspect of the present invention, there is provided a liquid filled type vibration isolator as set forth in the first aspect of the present invention, wherein a third liquid chamber is provided between the first diaphragm and the main chamber and a second orifice through which liquid flows is provided between the third liquid chamber and the main chamber.
With this arrangement, according to the present invention, the second orifice is prepared for mainly isolating the engine idling vibration, and the first orifice is prepared for absorbing and isolating the engine shake, thereby it is possible to efficiently absorb and isolate both engine shake and engine idling vibration.
Further, according to a third aspect of the present invention, which is similar to the first aspect of the present invention, there is provided a liquid filled type vibration isolator as set fort in the first aspect of the present invention, wherein liquid in the first orifice and liquid in the second orifice are associated with each other in response to a specific frequency.
With this arrangement, according to the present invention, the dynamic spring constant in this liquid filled type vibration isolator is reduced over a full frequency range in its entirety, and a reduced (bottom) range of the dynamic spring constant in each of two specific frequency ranges within an engine idling frequency range. As a result, it is possible to aim at reducing the dynamic spring constant even in a vibration range during idle-up due to operation of accessories, in addition to the engine idling vibration. That is, it is possible to cope with isolation of vibration in both cases of normal idling vibration and vibration during idle-up.
Next, according to a fourth aspect of the present invention which is similar to any of the first to third aspects of the present invention, there is provided a liquid filled type vibration isolator as set forth in any of the first to third aspects of the present invention, wherein the first diaphragm and the second diaphragms are integrally incorporated with each other.
With this arrangement, according to the present invention, it is possible to aim at reducing the costs of manufacturing two diaphragms, that is, the first and second diaphragms. As a result, it is possible to aim at reducing the costs of manufacturing the liquid filled type vibration isolator in its entirety. Namely, for example, the two diaphragms can be molded in a bundle by a suitable molding means, thereby it is possible to reduce the total manufacturing costs including a cost for parts control.
Next, according to a fifth aspect of the present invention which is similar to any of the first to fourth aspects of the present invention, there is provided a liquid filled type vibration isolator as set forth in any of the first to fourth aspects of the present invention, wherein a sealed air chamber is formed making contact with the first diaphragm and defined by a space in which air is hermetically sealed, and a third diaphragm is also provided forming a one of walls of the sealed air chamber while an auxiliary chamber adapted to operate the first and second diaphragms which define the above-mentioned sealed air chamber is provided for selectively introducing negative pressure or the atmospheric pressure.
With this arrangement, according to the present invention, the following effects can be exhibited: That is, in the present invention, only one orifice can exhibit a damping function for engine shake, and liquid is resonated in the orifice in order to cope with engine idling vibration, thereby it is possible to aim at reducing the dynamic spring constant in this vibration frequency range. As a result, two vibration damping functions, that is, for example, damping of engine shake and damping of engine idling vibration, can be exhibited. Further, the dynamic spring constant of the liquid filled type vibration isolator can have a generally high value in such a case that both chambers are in a vacuum suction condition, but an extreme increase in the dynamic spring constant in a frequency range slightly deviated from a specific frequency can be restrained by the action of the abovementioned sealed air chamber.
With this arrangement, it is possible to avoid extremely increasing the dynamic spring constant even though the idling speed of the engine varies (increases) upon engine idle-up, thereby it is possible to aim at absorbing and isolating idling vibration upon engine idling up.
Next, according to a sixth aspect of the present invention which is similar to any of the first to fifth aspects of the present invention, there is provided a liquid filled type vibration isolator as set forth in any one of the first to third aspects of the present invention, wherein a partition member and a metal member combined with this partition member are formed by pressing a metal sheet, and these two members hold therebetween the first and second diaphragms so as to secure them.
With this arrangement, according to the present invention, the following effects can be exhibited: That is, in the present invention, the partition member and the metal member can be formed by pressing a metal sheet, thereby it is possible to reduce the total manufacturing costs and lighten the total weight.